FAQs - Atex Explosion Hazards
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Frequently Asked Questions

How do I know my powder is explosive?

Dust explosibility classification (Group A/B) test using the Vertical Tube apparatus to determine whether the material falls within the scope of the necessary requirements for explosion protection of plant, buildings, etc

Group A (hazardous) – the dust cloud propagates flame from the ignition source and is classed as a combustible and potentially explosive material

Group B (non hazardous) – the dust cloud does not propagate flame from the ignition source and is classed as a non-combustible (non-hazardous) material. Happy Days!

If you are unfortunate enough to need further tests give us a call to discuss the range of tests appropriate to your needs.  Many clients have tests carried out which were not necessary for their project and by the time they come to us they realize more tests are needed.  We have over 42 years of experience in whats really needed.

Do I need to install explosion protection on my plant?

Whenever possible, the employer should prevent the occurrence of explosive atmospheres. Explosion risks must be assessed. In the event of an explosion, workers are at risk from uncontrolled flame and pressure effects in the form of heat radiation, flames, pressure waves and flying debris, and from harmful products of reaction and the depletion of the breathable oxygen in the ambient air. If all prevention measures have been exhausted, then protection measures must be employed to mitigate the consequences.

We have a large range of protection systems at our disposal, if we don’t make it ourselves, we can source it from colleagues within the industry who we know can do the job properly. With over 42 years of experience satisfying our clients needs, we know its best to sell solutions not just products to build client loyalty.

Why do I need explosion isolation?

In a system consisting of connected enclosures, a dust explosion ignited in one enclosure can propagate through the connection, generating increased turbulence, perhaps causing some pre-compression and then acting as a large ignition source in a connected enclosure. This combination of effects can enhance the violence of the secondary explosion and the protection requirements of the system thus need to be increased, or the enclosures isolated

Explosion isolation is achieved by a protective system, which prevents an explosion pressure wave and /or flame from propagating via connecting pipes or ducts into other parts of apparatus or plant areas. Systems providing complete isolation by operation of the isolation device(s) prevent the propagation of the flame as well as pressure effects. Systems providing partial isolation only isolate the flame propagation. This distinction is important for practical applications, because it is not necessary in all cases to achieve a complete isolation of flame and pressure. In some cases it is sufficient to achieve only flame isolation.

ATEX Explosion Hazards Limited has worked in the Dairy, Food, Chemical, pharmaceutical, cement, power, biomass and waste.  We don’t just know about our own products but we know our clients processes and safety challenges.  We network, sit on standards committees, attend industry seminars and keep up to date with industry trends.

“Competent persons are persons with comprehensive expertise in explosion protection as a result of their professional training, relevant experience and current professional activity.”  There are many paths an explosion can take, some are during abnormal operations, we have been around long enough to know most of them.

What size of vent do I require on my vessel?

Accurate sizing of vents is the most important aspect of vent design. The size of the vent depends on the explosion characteristics of the dust, the state of the dust cloud (concentration, turbulence and distribution, filling), the geometry of the enclosure and the design of the venting device. The two principal explosion characteristics of the dust are the maximum overpressure Pmax and the dust explosion constant Kst.

For cubical enclosures, Pmax and Kst are essentially independent of enclosure volume. The volume of the enclosure and the length-to-diameter ratio L/D relevant to the shape of the enclosure and the position of the explosion vent are required for sizing vents. The explosion resistance of the enclosure Pred, max is also required for vent sizing. All parts of the enclosure, e. g. valves, sight-glasses, man-holes and ducts that are exposed to the explosion pressure shall be taken into account and the explosion resistance of the weakest part shall be taken as the explosion resistance for the enclosure.

The two principal vent device parameters are the static activation over pressure Pstat and the venting efficiency of the venting device.

Many times clients will decide to reduce the pressure resistance of their vessel because they do not know the strength of their vessel, this can have very expensive consequences. We know the most cost effective ways to get that information and whither its worth it.

What is the effect of a vent duct?

If the pressure venting device is activated and there is a vent duct downstream of the system, such a duct can be filled with an explosive mixture before the flames exit the protected vessel. This will result in a secondary explosion in the vent duct, which in turn, hinders the venting process. Therefore, the maximum reduced explosion over pressure inside the vessel will increase with the increasing length of the vent duct. Vent duct should be equal to the Cross Sectional area of the vent, a straight as possible without a bend greater than 20 degrees or any other obstruction to hinder its venting.

Many times equipment is sold to a client by a third party not always the OEM.  The end-users contracts a fabricator who may be skilled in air-conditioning but not explosion protection. If you have any concerns please call us, we do not charge for simple advice.  Its in our best interest that our countries industry is a safe place to work and that all explosion protection measures are properly designed.

How do I block the end of explosion vent duct?

To prevent the ingress of rain, snow or other unwanted visitors into the vent ducts, light covers, e.g., foils/films or disks in clamping profiles are admissible less than 0.5kg/m2. The open of the devices should be at very low static activation over pressures of Pstat < 0.05 barg. The covers shall not affect the venting process or endanger people or materials.

We have a whole powerpoint presentation on called “Oops-What happens when it goes wrong” and this problem is the highest on our list of Oops.  Give us a call and we can forward you.

What is a safe vent area?

Explosion venting is always accompanied by flame propagation plus pressure consequences in the surrounding areas. The reason for this is the unburned product, which is pushed outside once the vent system actuates. The fuel-air-mixture generated externally is then ignited by a flame jet exiting the vent area. Dependent on the volume of the equipment it can reach up to 60 m. The venting process should not endanger personnel, the operation of any equipment and should not be restricted. This shall be considered when designing the plant and may be accomplished by releasing the pressure upwards, which is effected by gravity, i.e. length of flame = 8 x V 1/3 in m or horizontally length of flame = 10 Volume 1/3 in m, which usually causes bigger problems in a congested complex. Larger fireballs have been observed during vented dust explosion in cases where additional dust deposits accumulated in the vicinity of the vent opening.

We can offer a full range of options from flame diverters, flameless venting or suppression which may save you a lot of financial trouble in the short or long term.

Will my rotary valve act as an explosion isolation device

Rotary valves shall only be used as “explosion barriers” for enclosures. The effectiveness against flame propagation (minimum explosion safe Gap) and their pressure rating shall be ATEX certified. After an explosion the rotary valve shall be stopped automatically to prevent transfer of glowing material.

If the Rotary valve is not ATEX certified or fails to fulfill the ignition breakthrough requirements due to wear and tear, a product plug having an adequate height, is suitable in combination, as an Isolation system.   The product layer height must be ensured by a level indicator, that under the pressure stress of the explosion, no flames can pass through the product. Level indication must be ensured as fail safe and as a double knock system by operation.

Many clients have replaced rotary valves for explosion barriers to save costs in industries where wear and tear costs more than originally desired. Competency is more about experience when it comes to cost effective safer design.  Many things are complaint when installed new but 6 to 12 months down the road the issues come to the fore.  Please call us first to save you this painful experience.

Can I vent inside my building?

When an explosion vent opens as a result of a dust explosion, a fireball or jet of flame must be expected. This can carry out a mass of burning and unburnt dust. In addition there will be a pressure wave associated with the explosion. If the vent opens inside the building the burning dust may start further fires, and the blast may damage nearby plant. Anyone inside the room or building may be at serious risk. For these reasons explosion vents which discharge inside a building will give people inside the building little protection from the explosion. The usual solution is to fit a duct to lead the explosion products to a safe place in the open air. You may need to keep personnel away from an area around the end of a vent duct.

We think after 42 years we have seen it all.  A recent client had a cyclone in the middle of a large room the flame was only 15m long, 5m short of the roof and 6m wide when the nearest walkway was 10m away.  The vent would only cost 500 euro but the pressure from the secondary explosion in the room would have been from 168 mbar at the epicenter to 32 mbar 20 meters away! At 30 mbar you will break glass and cause minor structural damage, never mind the damage to personnel.  The client has now purchased a flameless vent for 5,000 euro 🙂

Can I use a Flameless Vent inside my building?

Proprietary flameless venting devices, which quench flames and catch burning dust, are certified for use inside a building. The flameless vents do have restrictions on their use due to the back pressure they cause in quenching the flame and filtering the majority of the burning dust. There will be room volume restrictions for exhausting the unburnt gases and a safe area which should not be populated by a permanent work station and loose flammable material. The supplier’s’ advice concerning installation must be followed carefully.

We have been installing flameless vents for many years now and have listened to our clients and seen how they survive various environments.  Check out our new revisions with improved features which open flameless vents to a wider range of applications, especially those requiring higher hygiene requirements. and serviceability.

How do I become ATEX COMPLIANT?

You have to be very careful about ATEX compliance as there are 2 forms

The ATEX 95 directive or the product directive 94/9/EC is for equipment and protective systems for use in potentially explosive atmospheres. This qualifies you to place your products on the market by different categories suitable for specified Explosion Zones. If may be self certified for the lower risk categories otherwise you will need Notified body approval. One must be very careful about the difference between component approval and system approval. Having a component such as a sensor on a simple assembly such as a silo or a vent panel does not automatically give you system approval. Many suppliers have added the certificate of a component(s) in an assembly and are claiming system approval.

The ATEX 137 directive or Users directive 99/92/EC is for the introduction of measures to encourage improvements in the safety and health of workers at work in explosive atmospheres.

  • preventing the formulation of explosive atmospheres where this is possible
  • preventing the ignition of explosive atmospheres
  • mitigating the detrimental effects of an explosion so as to ensure the health and safety of workers and where necessary
  • preventing propagation of explosions

The end user is responsible to ensure the overall explosion safety of their facility which must be verified by competent person before use. We always recommend that you employ the services of a consultant with a track record in explosion technology but also experience in your particular industry. Always remember people and their actions cause explosions, zoning and system approvals does not make you any safer if your workers have not been properly trained.

What forms of Explosion Prevention are available?

The first part of good explosion prevention is to have proper and detailed data on the Flammability and Ignition characteristics of your hazard, be it gas, powder or vapours. Once you know your product you need to consider appropriate safety measures. Prevention measures such as avoidance of the identified ignition sources in your plant, the selection of the proper equipment for your designated explosion zones. You may still decide that you need prevention safety equipment to reinforce your safety measures, such as Inert gas blanketing to reduce O2 levels or spark detection and extinguishing, temperature monitoring or gas monitoring such as the ATEX CO monitoring system which is very popular in the Dairy powder drying industry. Ultimately a well trained workforce is your ultimate prevention measure.

A well trained employee is as important as a well informed employer.  We can offer  presentations on the basics of explosion safety, application driven, suited to your industry.  We want to share our experience with you to make a safer industry.

Can you help me with my risk assessment?

We have over 42 years of explosion safety experience in a wide range of industries. We can send out the appropriate consultant verified by us to meet your industry needs.

What’s this Hot Water Explosion suppression about?

During the 1970’s and 80’s the Dairy industry had a very big problem with existing protection options. Hygiene and personnel safety was becoming a bigger issue, especially for their large volume Dryers up to 1000m3. Explosion venting inside the building was common and if venting was not possible especially on Fluidbed and cyclones. Chemical suppression with 60 bar powder bottles opened by explosively actuated rupture discs was unacceptable. Pressure Hot Water Explosion suppression used 10 bar hot water bottles at 184C releasing through pyrotechnically actuated lockable valves. When released the water instantly dropped to less than 100C flashing off 1600 times its original volume via its excess pressure and temperate into 16% steam and 84% micromist water droplets small enough to instantly quench and wet the milk powder fire ball. After system activation the bottles did not need to be removed only valves reset, refilled and the heat turned back on.

Why do I need an explosion door, they are so expensive?

Although explosion doors were the main type of explosion venting device they are now been replaced with more sophisticated vent panels which in their most basic form are relatively cheap flat single profiled stainless steel discs stitch cut on 3 sides and release at typically 100mbar with virtually 100% efficiency. This gets more expensive as you have higher pressure fluctuations, vacuum resistance issues, temperature and personnel safety as you cannot walk on a vent panel. If they fire they stay open allowing oxygen into the subsequent fire and have to be disposed and replaced by spares. Explosion doors can be self reclosing, endure all the conditions described above and can be reclosed after the event. They are still very common on the cement and steel industries where such problems are unacceptable.

We use our 42 years of experience to make you a safe ATEX compliant company